Aero 2 is a good damage spell, same cast time as stone 3 and more potency.
Areo 3 takes longer to cast and more mp, but it has the most potency and is aoe.
Aero has 10 less potency and is really efficient mp wise, and is insta cast which allows you to weave in assize and fluid aura while waiting for gcd to cycle.

The dots from all 3 aero spells stack. All you need to do is switch out stone 3 for the appropriate aero spell when it is down, or when you have an off gcd spell up in the case of aero.